Water is very unevenly distributed on Earth. Long-term droughts, and major floods happen randomly; deserts hardly ever get any water. Two out of six billion people, need more water on land; while fresh melt water from ice caps is raising ocean levels. The Los Angeles Times (1966) had a chart showing 280 cubic miles of water evaporated every day; 230 from sea, and 50 from land. The water precipitates as rain somewhere else (70 on land, with 20 runoff to the sea, and 210 on the sea). 280 cubic miles equals 0.01% of Earth's 320 million cubic miles of water.
97% of our water is too salty for crops or people, and 2% (7 million cubic miles) is frozen in ice caps. Several sources say that ocean's are rising 2 millimeters (0.08 inch) per year. This much over 140 million square-miles of ocean equals 200 cubic miles of melt water. One cubic mile of water equals one trillion gallons; 200 trillion gallons melt from the ice every year.
America used 150 trillion gallons (500,000 per person) in 2000. At this rate, the world would need 3000 trillion gallons, or 3000 cubic miles of water per year. Earth's land area, 50 million square miles gets 70 cubic miles (70 trillion gallons) water/day; 3000 trillion would take only 45 days of rain. The US 150 trillion gallons on our 3 million square miles would take about 38.
This is lots of water, but uneven supply, due to climate change leads to droughts, floods, critical water shortages in many countries. Conservation, and better water management will always be necessary. Nuclear plants could give energy for desalination and purification of sea and poor quality ground water by reverse osmosis throughout the world.
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